Hitherto, a fluorescent whitening process has been generally used for the purpose of increasing whiteness of a finished photographic printing paper. As compounds having such a fluorescent whitening effect, a great number of compounds are known and various methods of using them are also known.
One method is to add a fluorescent whitening agent to a paper base. In another method, a fluorescent whitening agent is added to a development processing solution, whereby it is applied to the printing paper in a development processing step. Further, it is known to add the fluorescent whitening agent to a light-sensitive material by blending it with a hydrophilic vehicle of a layer of the light-sensitive material.
In the case of adding a fluorescent whitening agent to the base, if it is applied to a polyethylene laminated paper base, there are problems in production, namely, the fluorescent whitening agent is easily thermally decomposed when it is added to a laminate layer fusing at high temperature.
In incorporating the fluorescent whitening agent in a development processing bath, there are problems in that it is not only difficult to use (because development conditions should be precesely controlled to retain the fluorescent whitening effect of the finished product constant) but also this procedure generally does not sufficient emphasize the white background of the prints. From such viewpoint, adding the fluorescent whitening agent to a hydrophilic vehicle of the light-sensitive material is preferred.
As fluorescent whitening agents used for this last method, there are, for example, sulfonated stilbene whitening agents as described in U.S. Pat. No. 2,933,390, Japanese Patent Publication No. 30495/73 and Japanese Patent Application (OPI) No. 135833/80 (The term "OPI" as used herein refers to a "published unexamined Japanese Patent Application".), etc., as water soluble agents. As water insoluble agents, stilbene type, coumarone type and thiophene type whitening agents are widely used. In the case of water soluble fluorescent whitening agents, it is advantageous to use the same together with a water soluble polymer such as polyvinyl pyrrolidone as described in Japanese Patent Publication No. 7127/59 or Research Disclosure, No. 17159 to prevent the fluorescent whitening agent from flowing out of the layer during development processing and in any subsequent water washing step, or to alter the molecular structure of the fluorescent whitening agent so that the same hardly flows out as described in Japanese Patent Application (OPI) No. 32547/81 (corresponding to U.S. Pat. Nos. 4,336,326 and 4,302,579) or European Pat. No. 0024380B1.
Examples of the water soluble fluorescent whitening agents used as described above include the following. ##STR2##
On the other hand, it is well known to carry out spectral sensitization to adapt a photographic printing paper for, for example, high speed monochromatic for photo-type setting use or color prints, etc. In order to carry out spectral sensitization, many sensitizing dyes, including cyanine and merocyanine dyes, have been put in practical use.
It is also important to shorten the time of development processing from the viewpoint of compensating for the fault of silver halide photographic systems of requiring high labor and substantial time for development processing as compared with other recording material. However, with the wide use of laminated paper as a printing paper base and the use of rapid development processing with automatic development devices, spectrally sensitized printing paper sometimes causes the problem of residual color due to sensitizing dyes which deteriorates the whiteness of the finished print. Particularly, in high temperature rapid development processing, especially with short time processing where the washing time is 30 seconds or less, residual color due to sensitizing dye(s), not heretofore a serious problem, has become a problem.
On the other hand, in order to overcome the problem of residual color caused by rapid processing, there is a technique of increasing apparent whiteness using water soluble fluorescent whitening agents as described in, for example, Japanese Patent Application (OPI) No. 135833/80.
However, the present inventors found that whiteness is deteriorated by incorporating a water soluble fluorescent whitening agent in a hydrophilic vehicle because residual color due to sensitizing dyes can increase depending upon the kind of sensitizing dye(s) used.
Further, it has been found that this last mentioned problem is related to the conditions of fixing processing and it remarkably occurs in the case of carrying out acid hardening fixing using polyvalent metal salts such as alum, etc.
It was unexpected that fluorescent whitening agents would increase residual color with certain kinds of sensitizing dyes and it has not heretofore been known what combination of structures cause such problem.
Further, in the case of using sensitizing dyes of the present invention as described hereinafter, when the fluorescent whitening agents of U.S. Pat. No. 2,933,390, Japanese Patent Publication No. 30495/73 and Japanese Patent Application (OPI) No. 135833/80 are added to the hydrophilic vehicle, residual color remarkably increases regardless of the layer to which they are added. However, in case of merocyanine dyes, such as phenomenon is not observed. Accordingly, it is believed that the increase in residual color is a peculiar phenomenon with cyanine dyes. Of the cyanine dyes, those which have only substituents having a low molecular weight and have at least one sulfoalkyl group are suitable for rapid processing because they seldom cause residual color. However, such dyes normally cause a remarkable increase in residual color in combination with a fluorescent whitening agents.